The conversion of acids and alcohols to esters is well known, as is the conversion of esters to acids and alcohols. The conversion of many esters to acids and alcohols can be carried out by boiling the ester in a mixture of base and alcohol. However, the conversion of polyesters to their corresponding monomeric acids and glycols is very difficult. Polyesters are normally not soluble in the solvents that are used for the conversion of esters to alcohol and acid. Also, polyesters are often highly crystallized, further limiting their solubility and hindering the attack of the ester bonds by a base.
Methods are known for the conversion of some polyesters to their monomeric components. These depolymerization methods are generally used to recover monomers from polymer scrap for the repolymerization of the monomers, but can also be used to analyze the polymers to determine their monomer content.
Polyesters can be converted or depolymerized to amides and glycols by a process known as aminolysis. This process entails the refluxing of a polyester with a primary amine or hydrazine such as disclosed in ASTM Method D 2456 and, Anal. Chem. 34 (1962)1173 G. G. Esposito. However, the aminolysis process is generally slow and produces undesirable side reactions with some polyesters.
The transesterification of polyesters is another method of depolymerizing polymers. This method entails heating a polyester in excess alcohol or glycol, optionally in the presence of a catalyst such as disclosed in ASTM Method D 2455 and in Anal. Chem. 37 (1965)1709 J. Jankowski and P. Garner. The transesterification process, however, is generally very slow and high temperatures and pressures are needed to achieve practical conversion rates.
Another method of depolymerizing polyesters is by hydrolysis. This process entails the heating of a polyester with a base in the presence of a solvent, such as an alcohol, such as disclosed in Anal. Chem. 37 (1965)1306, J. R. Kirby, A. J. Baldwin, and R. H. Heidner; U.S. 4,605,762, and U.S. 4,620,032. Hydrolysis, however, is also generally slow at mild conditions, thus, requiring high temperatures and pressures to achieve rapid conversions.
In spite of the many known depolymerization processes, polyesters are not easily depolymerizable by any known process at ambient conditions.
In light of the above, it would, therefore, be very desirable to rapidly convert polyesters under relatively mild conditions of temperature and pressure without generating undesirable side reactions.